1. Field of the Invention
The present invention generally relates to an apparatus for controlling an H-bridge DC-AC inverter and, more particularly, to an apparatus for controlling an H-bridge DC-AC inverter using a voltage feed-forward compensation configuration to calculate respective voltage feed-forward compensation parameters under a mode and a buck mode to control the output current waveforms for better performance of a power regulator. Moreover, an AC output current is used as a feed-back control signal to control the output waveforms of the power regulator. Furthermore, the control signals of active switching elements in the DC-AC inverter is synchronous with the AC current so as to reduce the switching loss, ripple current and improve the power conversion rate. The DC-link capacitor can be removed since the ripple current is reduced, which makes the DC-AC inverter more compact.
2. Description of the Prior Art
The H-Bridge DC-AC inverter converts unstable DC distributed power and renewable power into stable DC power and then inverts the DC power into AC power to be used with the AC utility.
Please refer to FIG. 2A and FIG. 2B, which are circuit diagrams of a conventional apparatus for controlling an H-bridge DC-AC inverter and a conventional control configuration thereof. A DC voltage Vdcbus is fed into a proportional-integral regulator 31 outputting an output signal joined by a DC current idc to enter another proportional-integral regulator 32. The output signal is introduced into the positive input terminals of two comparators 35, 36, while a first high-frequency triangular wave is introduced into the negative input terminal of the first comparator 35 and a second high-frequency triangular wave is introduced into the negative input terminal of the second comparator 36. An output signal from the first comparator 35 is capable of controlling the gate of a first active switching element, and an output signal from the second comparator 36 is capable of controlling the gate of a second active switching element.
An AC current iAC is introduced into a proportional-integral regulator 33 to output an output signal entering the positive input terminal of a comparator 34 and the negative input terminal of the comparator 34 receives a high frequency triangular wave so as to generate an output signal capable of controlling the gates of a third active switching element, a fourth active switching element, a fifth active switching element and a sixth active switching element.
Such an H-bridge DC-AC inverter exhibits a wide operation range (Vinmax/Vinmin) so that there is flexibility in circuit design. However, switching loss such as turn-on loss and turn-off loss may result from hard-switching since active switching elements are used. Moreover, during hard-switching of the switches, switching surge occurs to shorten the lifetime of the switching elements.
Therefore, there is need in providing an apparatus for controlling an H-bridge DC-AC inverter to reduce the switching loss, improve the conversion rate and prolong the lifetime of the switching elements.